1. Field of the Invention
The present invention relates to an operational amplifier, and more particularly, to an operational amplifier of a source driver and method thereof.
2. Description of the Prior Art
Liquid crystal display (LCD) devices are flat panel displays characterized by their thin appearance, low radiation and low power consumption. LCD devices have gradually replaced traditional cathode ray tube (CRT) displays, and have been widely applied in various electronic products such as notebook computers, personal digital assistants (PDAs), flat panel televisions, or mobile phones. An LCD device usually includes an LCD panel, a timing controller, a gate driver, and a source driver. The timing controller is used for generating image data signals, together with control signals and timing signals for driving the LCD panel. The gate driver is used for generating scan signals for turning the pixel circuits on and off, and the source driver is used for generating driving signals based on the image data signals, the control signals and the timing signals.
Normally, a driving capacity and a slew-rate of an operational amplifier of a source driver is related to its bias current I1 and its compensation capacitor CC. In other words, the slew-rate of the operational amplifier is limited by I1/CC. In order to improve the driving capacity and the slew-rate of the operational amplifier, the bias current I1 needs to be increased or the compensation capacitor CC needs to be decreased or directly removed. If the compensation capacitor CC is directly removed, the operational amplifier becomes unstable in a high-impedance state. Therefore, the operational amplifier presently needs to be improved to solve the limited slew-rate issue and the instability issue without increasing the bias current I1.